Map reduce works great and is an awesome feature. I've noticed however when writing them the only error message I seem to get is:

failed with error "db assertion failure"

But it doesn't show the line number or error in the js. This can make it a bit tough to debug the javascript - I usually just end of deleting things (guess and check) until it works, which works. But was just curious if there was a better way to see the errors in the javascript while debugging. Thanks!